In the oil and gas exploration and extraction industries it is often desirable to be able to modulate downhole pressure when required. For example, it is desirable to isolate a section of well bore to create sections of differential pressure within the bore. A sealing device is used to create a seal within the bore, such that fluid pressure on one side of the seal increases relative to fluid pressure on the other side. Further, a temporary decrease in well pressure can be used to initiate flow from the reservoir in a process known as ‘swabbing’. One means of doing this is to make use of a swab cup, which is a cup-shaped resilient member which is lowered on a mandrel into the well. As a pressure differential develops across the cup, the walls of the cup are pushed into contact with the well tubing or bore wall, thereby sealing a portion of the well. Thus, the pressure below the cup may decrease, while the pressure above may increase.
Similarly-constructed pressure cups are also used in a wide variety of other sealing and fluid lifting applications. For example, variations in pressure may also be used to actuate or to control other downhole tools and instruments which rely on fluid pressure for their operation. Conventional cups are constructed with an outer diameter slightly larger than that of the bore, such that a seal is present even when the cup is not inflated.
Conventional pressure cups suffer from a number of disadvantages. For example, as the cup is constructed with an outer diameter slightly larger than the diameter of the bore, the cup will rub against the bore as it is run into position. This can wear the cup and may affect the formation of a seal between the cup and the bore wall. Furthermore, if the bore has restrictions which narrow the width of the bore, it may not be possible to pass the restriction without damaging the pressure cup and an alternative sealing mechanism is required.